Immunosuppressive constituents from Urtica dentata Hand

A novel biscoumarin, 6,6′,7,7′-tetramethoxyl-8,8′-biscoumarin (1), was isolated from the ethyl acetate extract of Urtica dentata Hand, together with five known compounds named as 7,7′-dihydroxy-6,6′-dimethoxy-8,8′-biscoumarin (2), 7,7′-dimethoxy-6,6′-biscoumarin (3), scoparone (4), vanillic acid (5), and daucosterol (6). Structures of the isolated compounds were elucidated on the basis of spectroscopic analysis including 2D NMR experiments. Compounds 1 and 2 were confirmed to be a rare carbon–carbon linked symmetrical biscoumarin. Compounds 1–4, especially 1 (IC50 = 8.18 × 10− 5 mol/l), showed potent immunosuppressive activities as determined by the Cell Counting Kit-8 assay for lymphocyte proliferation. Also, in the FACS analysis, 1 (IC50 = 5.19 × 10− 4 mol/l) promoted the differentiation of CD4+CD25+Foxp3+ T regulatory cells distinctly compared to the normal control. Thus, 1 possessed specific immunosuppressive property by eliciting T regulatory cells, which may provide a potential treatment strategy fo...